As a resin composition containing a fiber and an olefin polymer, JP 03-121146A discloses a long fiber-reinforced polyolefin resin composition for making a molded article, containing a polyolefin, a modified olefin polymer and a fiber, wherein substantially all of the fibers are 2 mm or longer in their length, and are arranged nearly in parallel with one another; JP 2009-292861A discloses a molded article of a resin composition containing a matrix polymer, a modified polymer and an organic polymer fiber which carries on its surface a substituted group capable of a condensation reaction with a carboxyl group or an acid anhydride group of the modified polymer; and EP 2236547A (corresponding to WO 2009/093748) discloses a resin composition which contains (A) a surface-treated fiber comprising a polyalkylene terephthalate fiber and/or polyalkylene naphthalene dicarboxylate fiber and a sizing agent adhered to the surface of the fiber, and (B) a polyolefin resin modified with an unsaturated carboxylic acid and/or an unsaturated carboxylic acid derivative.